The present invention relates to compositions, methods and kits for use in the purification of contaminated drinking water for purposes of rendering it potable. The compositions and kits are especially designed for personal or domestic use in the batchwise purification and clarification of relatively small predetermined volumes of contaminated drinking water. The compositions and kits are also designed for personal or domestic use in the purification and nutrification of contaminated drinking water.
There is a need for potable water in all areas of the world. In developed countries, water is purified and potable water is supplied on a large scale, typically by large national or multinational water management companies. This water is typically supplied directly to the consumers homes in a potable form. However, in some parts of the world, for example in some rural areas of developing countries, many people either do not have a direct water supply to their homes and only have access to a non-potable communal water supply such as a village well, or cannot be guaranteed that the water they do receive is potable. As a result, considerable numbers of people die each year as the direct result of drinking contaminated drinking water. Thus, there is a need for water purification kits and compositions that allow the consumer to purify their own water, which produces potable water in a fast and efficient manner.
Current water purification compositions available on the market to date, consist mainly of disinfectants, e.g. sources of chlorine and/or iodine, and do not adequately purify water. Water which is obtained after treatment by these water purification kits, may still comprise amounts of water impurities, e.g. heavy metal ions such as arsenic, which, when continually consumed for a prolonged period of time, may lead to health problems. Thus, there is a need to provide a water purification composition which removes water-impurities like heavy metal ions including arsenic and lead, more efficiently and effectively than current water purification kits.
It has now been found that water purification compositions based on certain combinations of inorganic coagulants and water-soluble or water-dispersible polymers remove greater amounts of water impurities, such as heavy metals, from water compared to current water purification compositions.
Also, current water purification compositions do not adequately remove, kill or inactive micro-organisms such as bacteria, viruses and cysts, which are present in the water. Thus, there remains a need to provide a water purification composition which does adequately remove, kill or inactive these micro-organisms.
It has now been found that when the composition of the present invention comprises a disinfecting agent, the composition removes, kills or inactivates a surprisingly larger amount of micro-organisms such as bacteria, viruses and cysts compared to water purification compositions known in the art.
In addition, the water which is to be purified by a water purification composition typically comprises a large amount of water-soluble organic content such as humic acid. With current water purification compositions, bleach, especially chlorine based bleach, can react with the water-soluble organic content and produce by-products in the water, including chlorine derivatives such as chloroacetic acid or chloroform, which are harmful to human and animal health. Thus, there is a need to provide water purification compositions, methods and kits which produce purified water comprising a low amount of disinfection by-products.
Another problem associated with the use of certain chlorine-based disinfectants such as calcium hypochlorite is that of product stability. In particular, it has been found that known compositions based on calcium hypochlorite can lose substantial disinfection efficacy under regular conditions of storage and use. Thus, there is a need for purification and disinfection compositions having improved storage stability.
After purification and disinfection of contaminated drinking water, there raises the further problem of maintaining the purity of the water until such time as it is required for drinking, whilst at the same time providing drinking water of satisfactory taste. Thus there is a need for compositions, methods and kits for purifying contaminated drinking water and which provides purified water having both longer life and improved taste attributes.
In addition to the need for purifying and clarifying contaminated drinking water, there is also a huge need in many parts of the world to improve standards of nutrition and health. The effective provision of both clean water and essential minerals and vitamins would clearly be of universal benefit but especially so in those parts of the world where potable water is in short supply. Thus there is a need for compositions, methods and kits for purifying and at the same time nutrifying contaminated drinking water.
The present invention relates to compositions, methods and kits for purifying and/or clarifying contaminated drinking water, as well as to compositions, methods and kits for purifying and nutrifying contaminated drinking water. In general terms, the compositions herein comprise at least a primary coagulant material and a so-called bridging flocculent material, the levels and ratios of coagulant to flocculent preferably falling within certain ranges. Highly preferred compositions also contain one or more of a coagulant aid, a microbiocidal disinfectant, a water-soluble alkali, a water-insoluble silicate (for example a clay, zeolite or mixture thereof), and a food additive or nutrient source.
According to a first aspect of the invention, there is provided a composition for purifying and clarifying contaminated drinking water and which comprises a primary coagulant, a bridging flocculent and a coagulant aid.
In preferred embodiments, the primary coagulant is selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof, for example, iron sulphate, iron chloride, aluminium chloride, aluminium sulphate, manganese sulphate, manganese chloride, copper sulphate, copper chloride, poly- variations thereof, and mixtures thereof. Generally, the compositions herein comprise from about 10% to about 99%, preferably from about 15% to about 50%, more preferably from about 25% to about 40% by weight of the primary coagulant.
The bridging flocculent on the other hand is preferably a high molecular weight water-soluble or water-dispersible polymer or mixture of polymers having a weight average molecular weight of at least about 2,000,000, more preferably at least about 5,000,000 and especially at least about 15,000,000. Bridging flocculents preferred for use herein are selected from the group consisting of water-soluble and water-dispersible anionic and nonionic polymers and mixtures thereof. Generally, the compositions herein comprise from about 0.1% to about 10%, preferably from about 0.2% to about 5%, more preferably from about 0.5% to about 3% by weight of the bridging flocculent
The term xe2x80x98coagulant aidxe2x80x99 herein refers to a water-soluble or water-dispersible polymer of lower molecular weight than that of the bridging flocculent and which aids the overall aggregation and flocculation process. The coagulant aid preferred for use herein is a low molecular weight, water-soluble or water-dispersible polymer which generally has a weight average molecular weight of less than about 1,500,000, preferably less than about 750,000 and especially less than about 300,000 and mixtures thereof. Generally the compositions herein comprise from about 0.1% to about 10%, preferably from about 0.5% to about 5%, more preferably from about 1% to about 4% by weight of the coagulant aid.
Although suitable coagulant aids include anionic polymeric hydrophilic colloids such as the carboxymethylcelluloses, highly preferred from the viewpoint of delivering excellent heavy metal, total soluble organic and cyst reduction performance are coagulant aids selected from the group consisting of water-soluble and water-dispersible cationic polymers and mixtures thereof, for example cationic polysaccharides of which chitosan is especially preferred. Preferred coagulant aids herein are substantially water-insoluble, having at least 10% by dry total weight of undissolved material as determined by the test described herein below, this being preferred from the viewpoint of providing compositions and methods delivering low total water-soluble organic content.
The weight ratio of primary coagulant to bridging flocculant herein is preferably from about 10:1 to about 200:1, more preferably from about 10:1 to about 150:1, yet more preferably from about 20:1 to about 100:1, and especially from about 25:1 to about 75:1, these ratios being valuable especially in conjunction with the levels of coagulant and flocculant described herein above for providing optimum purification performance in highly contaminated water conditions and for providing significantly improved rates of filtration and xe2x80x98non-blockingxe2x80x99 filter characteristics as well as excellent final product purity and clarity using paper and non-woven filters. Although the reasons for this improvement in filtration rate, non-blocking characteristics and product clarity are not fully understood, it is believed that higher levels and ratios of the bridging flocculant relative to the coagulant increases the xe2x80x98stickinessxe2x80x99 of the floes with a consequent reduction in colloidal particulates. Such compositions are also highly suitable for use herein in conjunction with cloth filters.
Thus, according to another aspect of the invention, there is provided a composition for purifying and clarifying contaminated drinking water and which comprises a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof; a water-soluble or water-dispersible polymeric bridging flocculent wherein the weight ratio of primary coagulant to bridging flocculant is from about 10:1 to about 150:1, preferably from about 20:1 to about 100:1, and more preferably from about 25:1 to about 75:1; and optionally a water-soluble or water-dispersible polymeric coagulant aid. The filtration characteristics of the composition can be assessed using a standard filtration test and are preferably such that at least one litre of treated model surface water after treatment with 620 mg/litre of purification composition passes a Whatman 1.21 xcexcm GF/C grade filter in less than 1 hour, preferably less than 45 minutes, and more preferably less than 30 minutes under ambient temperature conditions (20xc2x0 C.) and that at least 1 litre, preferably at least 2 litres, more preferably at least 3 litres of the treated water will pass the filter without blocking.
The model surface water described comprises:
(i) 24 mg/l humic acidxe2x80x94source of soluble natural organic matter;
(ii) 20 mg/l fine test dust(1-3 xcexcm)xe2x80x94designed to add turbidity;
(iii) 1500 mg/l saltxe2x80x94to give stress conditions of high total dissolved solids.
The resultant water has a high organic content ( greater than 10 mg/l total organic content (TOC)), high colour ( greater than 300 platinum cobalt units (PCU)), high turbidity ( greater than 15 nephelometric turbidity units (NTU)) and high total dissolved solids (TDS). The pH of the water is near neutral but can also be adjusted to pH 5 or 9 using HCl or NaOH respectively for stress testing. This water is referred to herein as xe2x80x98model surface waterxe2x80x99.
Compositions having optimum purification and clarification performance can also be defined by reference to the weight ratio of the primary coagulant and coagulant aid to the bridging flocculant. Thus, in preferred embodiments, the weight ratio of primary coagulant to coagulant aid is from about 8:1 to about 100:1, preferably from about 12:1 to about 30:1, and more preferably from about 15:1 to about 25:1. The weight ratio of coagulant aid to bridging flocculant, on the other hand, is preferably in the range from about 10:1 to about 1:6, preferably from about 5:1 to about 1:3, more preferably from about 3:1 to about 1:1.
The compositions, methods and kits of the invention also preferably comprise a microbiocidal disinfectant. Although a broad range of microbiocidal disinfectants are envisaged for use herein, preferred is a chlorine-based disinfectant. Calcium hypochlorite is especially preferred. Preferably, the compositions herein comprise primary coagulant and microbiocidal disinfectant in a weight ratio of from about 10:1 to about 100:1, more preferably from about 12:1 to about 60:1, and especially from about 15:1 to about 40:1. Generally, the compositions herein comprise from about 0.2% to about 10%, preferably from about 0.5% to about 4%, more preferably from about 0.7% to about 2.5% by weight of the microbiocidal disinfectant.
The compositions, methods and kits of the invention will also generally comprise a water-soluble alkali, this being valuable from the viewpoint of delivering an optimum in-use pH profile. In general terms, the levels of primary coagulant and alkali should be adjusted so as to provide a pH at in-use concentration (generally about 620 ppm of total composition) in the range from about 6.0 to 8.5, but preferably in the range from about 6.0 to 7.0, this being preferred from the viewpoint of providing performance robustness to contaminated waters of differing contamination levels and types. To achieve the requisite pH levels, the weight ratio of primary coagulant to water-soluble alkali will generally be in the range from about 0.8:1 to about 3:1, preferably from about 0.9:1 to about 2.4:1, and more preferably from about 1:1 to about 2:1. Generally, the compositions comprise from about 10% to about 45%, preferably from about 15% to about 40%, more preferably from about 20% to about 35% by weight of the water-soluble alkali.
The compositions, methods and kits of the invention can also include a water-insoluble silicate material such as a clay or zeolite which acts to aid the flocculation process by acting as a seed particle or by promoting absorption or cation exchange of metal ions. In preferred embodiments, the weight ratio of primary coagulant to water-insoluble silicate herein is from about 0.3:1 to about 5:1, preferably from about 0.7:1 to about 2:1, and more preferably from about 0.8:1 to about 1.2:1. Generally, the compositions herein comprise from about 10% to about 80%, preferably from about 20% to about 50%, more preferably from about 25% to about 35% by weight of the water-insoluble silicate.
The compositions and kits herein can utilized in a variety of forms and process types including batch and continuous, but preferably the composition is in unit dosage form and is used in the batchwise purification and clarification of a relatively small predetermined volume of contaminated drinking water. By relatively small volume is meant a volume of water typically required for immediate consumption in domestic or personal use, or which is required for short term storage and consumption. Typically, the compositions herein will be used for treating a volume of contaminated drinking water in the range from about 0.1 to about 100, preferably from about 0.5 to about 40, more preferably from about 5 to about 20 and especially from about 8 to about 13 litres. Unit dosage amounts of the composition, on the other hand, will generally range from about 50 to about 2000, preferably from about 100 to about 1000, more preferably from about 250 to about 750 mg per litre of contaminated drinking water. Unit dosage forms suitable for use herein include tablets, compacts, extrudates, water-soluble single and multi-compartment pouches etc but preferred unit dosage forms are single and multi-compartment sachets comprising a unit dose of granular or powdered composition which is opened prior to use and the contents emptied into a predetermined quantity of contaminated drinking water.
For the above purposes, highly preferred herein is a composition in unit dosage form comprising;
(i) from about 15% to about 50%, preferably from about 25% to about 40% by weight of the primary coagulant;
(ii) from about 0.2% to about 5%, more preferably from about 0.5% to about 3% by weight of the bridging flocculent; and
(iii) from about 0.5% to about 5%, more preferably from about 1% to about 4% by weight of the coagulant aid.
It is also important to ensure that in-use of the compositions, effective levels of the formulation ingredients are delivered to the sample of contaminated water to be purified. Thus the levels of primary coagulant, bridging flocculant and coagulant aid in composition should preferably be sufficient to provide by weight of the contaminated drinking water from about 50 to about 500, preferably from about 75 to about 300, more preferably from about 100 to about 250 ppm of primary coagulant, from about 1 to about 15, preferably from about 2 to about 10, more preferably from about 2.5 to about 7.5 ppm of bridging flocculent, and from about 1 to about 25, preferably from about 5 to about 20, more preferably from about 8 to about 12 ppm of coagulant aid.
In preferred embodiments, the microbiocidal disinfectant is incorporated in the compositions of the invention in a controlled, delayed, sustained or slow release form whereby the disinfectant is released into the drinking water and allowed to react with soluble organic impurities therein only after substantial completion of the coagulation and flocculation stage, this being valuable from the viewpoint of controlling and minimising the level of trihalomethanes (THM) generated during the purification process. A measure of the rate of release of disinfectant herein is tmax,, this being the time taken to achieve maximum residual disinfectant concentration after addition of the composition to deionized water at 20xc2x0 C. with gentle stirring. Preferably the compositions herein have a tmax, of at least about 1 minute, preferably at least about 2 minutes, more preferably at least about 4 minutes, and especially at least about 8 minutes. The rate of coagulation and flocculation of organic impurities, on the other hand, is measured by the n %-ile soluble organic matter flocculation rate (tn). The n%-ile soluble organic matter flocculation rate is defined herein as the time taken for n % reduction in the concentration of humic acid as measured according to the procedure described hereinbelow. Preferably, t80 for the compositions herein is less than about 2 minutes, preferably less than about 1 minute, more preferably less than about 30 seconds. In preferred embodiments, moreover, t90 for the compositions herein is less than about 2 minutes, preferably less than about 1 minute, more preferably less than about 30 seconds.
Thus according to another aspect of the invention, there is provided a composition for purifying and clarifying contaminated drinking water and which comprises:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a water-soluble or water-dispersible polymeric bridging flocculant; and
(iii) a microbiocidal disinfectant; and wherein the microbiocidal disinfectant is in controlled, delayed, sustained or slow release form whereby the composition has a tmax corresponding to the time for achieving maximum disinfectant concentration after addition to deionized water at 20xc2x0 C. which is greater than the 80%-ile soluble organic flocculation rate (t80) of the composition and more preferably greater than the 90%-ile soluble organic flocculation rate (t90) of the composition.
Preferably tmax is at least about 1 minute, more preferably at least about 2 minute, even more preferably at least about 4 minutes and especially at least about 8 minutes greater than t80 and preferably greater than t90.
The n%-ile organic matter flocculation rate is measured on the model surface water described herein above. 620 mg of the water-purification composition is added to a 1 litre sample of the model surface water with stirring. Aliquots of the liquid are then taken at 30 second intervals, each aliquot being filtered through a 0.45 xcexcm filter. The colour of the aliquot is then measured using for example a Hanna HI93727 colour meter and compared with a set of standards of known humic acid concentration and colour reading. The n%-ile soluble organic matter flocculation rate is the time taken to achieve a colour reading corresponding to a humic acid level which is (100-n) % of that of the initial level (24 ppm).
Preferably the final colour achieved (for example post-filtration at 30 minutes) using the purification compositions of the invention either in-vivo or on model surface water is less than 20 PCU, more preferably less than 15 PCU and especially less than 10 PCU. The final turbidity achieved using the purification compositions of the invention either in-vivo or on model surface water, on the other hand, is preferably less than 5 NTU, more preferably less than 2 NTU and especially less than 1 NTU, turbidity being measured using a Jenway 6035 turbidity meter calibrated daily against a 5.0 NTU standard.
In an alternative embodiment, the disinfectant and water-purification composition can be used in separate treatment steps, either simultaneously or sequentially with one another.
Preferably, the weight ratio of water-purification composition to disinfectant when used separately is from 10000:1, or preferably from 5000:1 or preferably from 1000:1, or preferably from 500:1, and preferably to 2:1, or preferably to 10:1, or preferably to 25:1, or preferably to 50:1, or preferably to 100:1.
The compositions, methods and kits of the invention also preferably comprise a food additive or nutrient source, this being valuable from the viewpoint of providing drinking water which is not only pure but which also contains essential minerals and other food additives necessary for good health and nutrition. The food additive or nutrient source can be included in the kits of the invention as one or more separate compositions in unit dosage form, or they can be incorporated directly into the water-purification composition itself.
Thus, according to a further aspect of the invention, there is provided a composition for purifying, clarifying and nutrifying contaminated drinking water and which comprises:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a water-soluble or water-dispersible polymeric bridging flocculant; and
(iii) a food additive or nutrient source.
In the case of food additives and nutrient sources which are non-coagulable or which at least partially survive the coagulation and flocculation process, for example fluoridating agents, iodinating agents, and essential minerals such as zinc and iron, the food additive or flocculent can be incorporated without special measures into the water purification composition. Otherwise, the food additive or nutrient sources can also be incorporated in controlled, delayed, sustained or slow release form as described herein with respect to the disinfectant. In this instance, the composition should have has a tmax corresponding to the time for achieving maximum nutrient concentration after addition to deionized water at 20xc2x0 C. which is greater than the 80%-ile soluble organic flocculation rate (t80) and preferably greater than the 90%-ile soluble organic flocculation rate (t90) of the composition.
It is also desirable herein to control the free moisture content of the water-purification compositions, especially in those compositions of the invention comprising calcium hypochlorite as microbiocidal disinfectant. It should be understood that many of the ingredients of the compositions herein such as the bentonite clays, alum based coagulants, etc contain a natural amount of free moisture and this has been found to be especially detrimental to calcium hypochlorite stability. In preferred embodiments, therefore, the compositions of the invention should have a free-moisture content of less than about 6%, preferably less than about 4% and more especially less than about 2.5% by weight thereof. It is also highly desirable to incorporate one or more ingredients which are capable of acting as a moisture sink, for example, low-moisture, pre-dried clays and hydratable salts in anhydrous or partly hydrated form whereby the free moisture content of the composition is maintained below the theoretical amount necessary for 100% hydration of the components of the composition. Particularly preferred moisture sinks include pre-dried clays and aluminosilicates, anhydrous sodium carbonate, and mixtures thereof. Preferably the moisture silks have a free moisture content of less than about 4%, more preferably less than about 3%, especially less than about 2.5% and more especially less than about 1.5% by weight. Free moisture content of the product or moisture sink is determined as follows. A 2 g sample of the product or moisture sink is extracted into 50 mls of dry methanol at room temperature for 20 mins. A 1 ml aliquot of this solution is then taken and the free moisture determined by a standard Karl Fischer titration. The free moisture is expressed as the percentage weight of water relative to the sample weight (in this case 2 g).
Thus according to another aspect of the invention, there is provided a composition for purifying and clarifying contaminated drinking water and which comprises:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a water-soluble or water-dispersible polymeric bridging flocculent;
(iii) calcium hypochlorite as microbiocidal disinfectant; and optionally
(iv) a moisture sink, and wherein the composition has a free-moisture content of less than about 6%, preferably less than about 4% and more especially less than about 2.5% by weight thereof.
The present invention also relates to methods for purifying contaminated drinking water comprising contacting the water with at least a primary coagulant material and a bridging flocculent material wherein the levels and ratios of coagulant to flocculent preferably fall within certain ranges. Highly preferred methods also comprise contacting the drinking water with one or more of a coagulant aid, a microbiocidal disinfectant, a disinfectant neutralization agent; a water-soluble alkali, a water-insoluble silicate (for example a clay, zeolite or mixture thereof), and a food additive or nutrient source.
Thus in a method aspect, the invention relates to a method for purifying and clarifying contaminated drinking water and which comprises contacting the contaminated water with:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a bridging flocculent selected from the group consisting of water-soluble and water-dispersible anionic and nonionic polymers having a weight average molecular weight of at least about 2,000,000, and mixtures thereof; and
(iii) a coagulant aid selected from the group consisting of water-soluble and water-dispersible cationic polymers having a weight average molecular weight of less than about 1,500,000, and mixtures thereof.
In a another method aspect, the invention relates to a method for purifying and clarifying contaminated drinking water and which comprises contacting the contaminated water with:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a water-soluble or water-dispersible polymeric bridging flocculant preferably selected from the group consisting of water-soluble and water-dispersible anionic and nonionic polymers, the polymeric bridging flocculent having a weight average molecular weight of at least about 2,000,000, and wherein the weight ratio of primary coagulant to bridging flocculant is from about 10:1 to about 150:1, preferably from about 20:1 to about 100:1, and more preferably from about 25:1 to about 75:1; and optionally
(iii) a water-soluble or water-dispersible polymeric coagulant aid preferably selected from the group consisting of water-soluble and water-dispersible cationic polymers, the polymeric coagulant aid having a weight average molecular weight of less than about 1,500,000.
The present invention further relates to a method for purifying, clarifying and nutrifying contaminated drinking water and which comprises contacting the contaminated water with:
(i) a primary coagulant selected from the group consisting of water-soluble, multivalent inorganic salts and mixtures thereof;
(ii) a water-soluble or water-dispersible polymeric bridging flocculant; and
(iii) a food additive or nutrient source.
The methods of the invention comprise a number of distinct chemical and physical stages which can run either concurrently or in sequence. In broad terms, these stages include
(i) a coagulation and flocculation stage in which the contaminated drinking water is brought into mixing contact with the coagulant, bridging flocculant and, if present, the coagulant aid so as to coagulate and flocculate the water impurities in the form of solid matter;
(ii) a disinfectant stage in which the drinking water is brought into microbiocidal contact with the disinfectant during or after substantial completion of the coagulation and flocculation stage;
(iii) a separation stage prior or subsequent to the disinfectant stage in which the solid matter is physically separated from the drinking water.
Preferably, the drinking water is brought into microbiocidal contact with the disinfectant after substantial completion of the coagulation and flocculation stage whereby tmax as hereinabove defined is greater than the 80%-ile soluble organic flocculation rate (t80) and preferably greater than the 90%-ile soluble organic flocculation rate (t90) of the composition.
In addition, the methods of the invention also preferably include a neutralization stage in which the drinking water is brought into contact with a disinfectant neutralization agent subsequent to said separation stage in order in order to maintain drinking water purity during storage of the drinking water but to reduce or remove excess disinfectant prior to use. In the case of chlorine-based disinfectants, suitable disinfectant neutralization agents include activated carbon and reducing agents such as sodium thiosulfate, sodium sulphite, hydrogen peroxide and sodium percarbonate.
Thus, according to a further aspect of the invention, there is provided a method for purifying and clarifying contaminated drinking water and which comprises subjecting the contaminated water to:
(i) a coagulation and flocculation stage in which the contaminated drinking water is brought into mixing contact with a primary coagulant, a polymeric bridging flocculant and, optionally a polymeric coagulant aid so as to coagulate and flocculate the water impurities in the form of solid matter;
(ii) a disinfectant stage in which the drinking water is brought into microbiocidal contact with a disinfectant during or after substantial completion of the coagulation and flocculation stage;
(iii) a separation stage prior or subsequent to the disinfectant stage in which the solid matter is physically separated from the drinking water; and (iv) a neutralization stage in which the drinking water is brought into contact with a disinfectant neutralization agent subsequent to said separation stage in order to reduce or remove excess disinfectant.
In addition, the methods of the invention also preferably include a nutrifying stage in which the drinking water is brought into contact with the food additive or nutrient source prior or subsequent to the separation stage.
Thus in a further method aspect, there is provided a method for purifying, clarifying and nutrifying contaminated drinking water and which comprises subjecting the contaminated water to:
(i) a coagulation and flocculation stage in which the contaminated drinking water is brought into mixing contact with a primary coagulant, a polymeric bridging flocculant and, optionally a polymeric coagulant aid so as to coagulate and flocculate the water impurities in the form of solid matter;
(ii) a disinfectant stage in which the drinking water is brought into microbiocidal contact with a disinfectant during or after substantial completion of the coagulation and flocculation stage;
(iii) a separation stage prior or subsequent to the disinfectant stage in which the solid matter is physically separated from the drinking water; and
(iv) a nutrifying stage in which the drinking water is brought into contact with a food additive or nutrient source prior or subsequent to the separation stage.
In the method aspects of the invention, the primary coagulant is generally added in an amount of from about 50 to about 500, preferably from about 75 to about 300, more preferably from about 100 to about 250 ppm by weight of the contaminated drinking water; the bridging flocculant is generally added in an amount of from about 1 to about 15, preferably from about 2 to about 10, more preferably from about 2.5 to about 7.5 ppm by weight of the contaminated drinking water; the coagulant aid is generally added in an amount of from about 1 to about 25, preferably from about 5 to about 20, more preferably from about 8 to about 12 ppm by weight of the contaminated drinking water; and the microbiocidal disinfectant is added in an amount of from about 2 to about 25, preferably from about 3 to about 20, more preferably from about 4 to about 15 ppm by weight of the contaminated drinking water. The volume of contaminated drinking water treated according to the methods of the invention is preferably in the range from about 0.1 to about 100, more preferably from about 0.5 to about 40, yet more preferably from about 5 to about 20, and especially from about 8 to about 13 litres.
Although any convenient method of separating the solid matter from the partially purified drinking water can be utilized, for example, by decanting, sedimentation, flotation, etc, preferably separation is accomplished by filtration in a separation stage using a paper, non-woven or cloth filtration element. Moreover, separation of the solid matter is preferably accomplished in a single filtration step without the need for change of the filtration element. It is a feature of the invention that the compositions and methods have superior filtration characteristics through disposable paper and non-woven filters and such filtration means may be preferred for optimum performance in removing cysts and bacterial contamination. The compositions and methods of the invention also provide superior filtration characteristics through cloth filtration elements made of a hydrophilic substrate such as cotton and such systems may be preferred from the viewpoint of cost and environmental considerations whilst at the same time providing highly effective filtration performance.
The compositions, methods and kits of the invention are particularly valuable in the purification of water which has been contaminated with heavy metals such as arsenic and/or lead and are effective in purifying water to an arsenic concentration below about 5 ppb, preferably below about 2 ppb and to a lead concentration below about 15 ppb, preferably below about 10 ppb.
The compositions, methods and kits of the invention are also valuable in the purification of water which has been contaminated with soluble organic impurities such as humic acid and are effective in purifying water to a total organic content below about 10 ppm, preferably below about 7 ppm and more preferably below about 4 ppm and to a trihalomethane (THM) level below about 100 ppb, preferably below about 70 ppb, more preferably below about 40 ppb.
The compositions, methods and kits of the invention are also valuable in the purification of water which has been contaminated with cysts such as Giardia and Cryptosporidium parvum and wherein the cyst concentration is reduced by a factor of at least about log 2, preferably at least about log 3, and more preferably by a factor of at least about log 3.5.
In a kit aspect, the present invention relates to a kit for purifying and clarifying contaminated drinking water and which comprises
(i) one or more unit doses of the water-purification composition herein, and
(ii) means for physically separating solid matter from drinking water.
The means for physically separating solid matter from drinking water includes cloth, paper and non-woven filters as described hereinabove.
The kits of the invention can additionally comprise one or more unit doses of a microbiocidal disinfectant composition and/or one or more unit doses of a food additive or nutrient composition. The microbiocidal disinfectant composition can be used with the water-purification composition either simultaneously or sequentially. Also the food additive or nutrient composition can be used with the water-purification composition either simultaneously or sequentially.